Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.26   4.724%   $213.9092   $213.91   $213.90   $213.90  
  Purchase #2 $19.73   4.378%   $20.5938   $20.59   $20.60   $20.60  
  Purchase #3 $72.40   5.540%   $76.411   $76.41   $76.40   $76.40  
  Purchase #4 $89.55   8.743%   $97.3794   $97.38   $97.40   $97.40  
  Purchase #5 $228.69   5.498%   $241.2634   $241.26   $241.25   $241.30  
  Purchase #6 $40.35   3.608%   $41.8058   $41.81   $41.80   $41.80  
  Purchase #7 $208.71   11.849%   $233.44   $233.44   $233.45   $233.40  
  7 purchase totals = $863.69       $924.8026   $924.80   $924.80   $924.80